JP5871240B2 - Optical element - Google Patents

Description

  The present invention relates to an optical functional technique such as a light modulation technique, a light receiving technique, an optical amplification technique, and a light emitting technique, and more particularly to an optical element having an optical functional element that can change the working light band by applying stress.

  Currently, with the increase in capacity of optical communication, it is required to increase the speed of the optical communication apparatus in the subscriber network in addition to the backbone network. In order to increase the speed of the optical communication device, it is necessary to increase the speed of the optical functional element, but at present, the optical functional element of a compound semiconductor is mainly used due to the demand for speed. However, since it is necessary to have a small size, low power consumption, and low cost for introduction into a subscriber network, development of an optical functional element using a cheaper silicon-based material is progressing.

  For an optical functional element using a silicon material, for example, in the case of an optical modulator, a configuration using free electron absorption by carrier injection (see Patent Document 1), a configuration using a Mach-Zehnder interferometer (see Patent Document 2). Further, there is a configuration using an electric field absorption effect of germanium (see Non-Patent Document 1). Among these, the configuration using the carrier injection and the Mach-Zehnder interferometer consumes a large amount of power, and it is difficult to meet the demand for low power consumption. On the other hand, the configuration using the electroabsorption effect can reduce power consumption, but germanium light absorption is limited to a long wavelength band of 1600 nm or more, and thus it has been considered difficult to use for optical communication. .

  However, in recent years, attempts have been made to expand the light absorption of germanium to the optical communication wavelength band by using the quantum effect. This has led to the possibility of realizing an optical modulator that operates at a high speed with low power consumption that can be used in a subscriber network. However, the optical band that can be modulated by one quantum structure is as narrow as several nm, and in order to cover the C band and the L band, it is necessary to create 10 or more types of quantum structures.

  On the other hand, there is a method of expanding a light modulation band that can be covered with one quantum structure by using a stress application structure (see Patent Document 3).

Japanese Patent No. 3957187 Japanese Patent No. 4429711 International Publication No. 2011/1/2968 pamphlet

Ning-Ning Feng, et al., “30GHz Ge electro-absorption modulator integrated with 3μm silicon-on-insulator waveguide,” Optics Express, Vol. 19, Issue 8, pp. 7062-7067 (2011)

  However, in order to form this stress application structure on the optical waveguide, it is necessary to use a rib-type optical waveguide whose optical confinement is weaker than that of the channel-type optical waveguide, and the minimum bending radius becomes as large as several hundred microns. . As a result, the driving voltage related to the stress application becomes as large as 100 V or more, the power consumption of the constant voltage source that supplies this driving voltage is large, and there is a problem that the power consumption cannot be reduced.

  As a technique for lowering the drive voltage related to stress application, there is a technique of introducing a stress concentration structure in applying stress. However, in a simple electrode structure, a phenomenon called pull-in occurs. This phenomenon is a phenomenon in which structural deformation abruptly progresses when a pull-in voltage is reached during boosting, and the deformation is not easily restored even if the voltage is lowered below the pull-in voltage. By pull-in, the hysteresis operation when the voltage level is repeatedly applied cannot be removed, and as a result, it becomes difficult to continuously control the stress value, resulting in a region where the desired stress cannot be realized.

  The present invention has been made in view of such problems, and an object of the present invention is to provide an optical element having an optical functional element that continuously varies the working light band over a wide range.

In order to solve the above-mentioned problem, the invention according to claim 1 is an optical element, wherein the substrate on which the first electrode is formed, and one end fixed to be spaced apart from the substrate are fixed. A beam portion having a constricted portion; an optical waveguide formed on the beam portion; an optical functional element formed on the optical waveguide located on the constricted portion; and a plurality of second optical elements formed on the beam portion. A plurality of second electrodes including a pull-in electrode and a stress control electrode having a width continuously changed with respect to a longitudinal direction of the beam portion, and the pull-in electrode; After applying a voltage to each of the pull-in electrode and the first electrode so that a predetermined potential difference occurs between the first electrode and the first electrode, the beam portion is pulled in, and the pull-in is generated. Each of the stress control electrode and the first electrode Features to control the stress by applying a voltage is applied to the optical functional element.

  According to a second aspect of the present invention, in the optical element according to the first aspect, the width of the pull-in electrode continuously changes in the longitudinal direction of the beam portion, contrary to the stress control electrode. It is an electrode.

  According to a third aspect of the present invention, in the optical element according to the first aspect, the pull-in electrode is located closer to the open end of the beam portion than the stress control electrode, and extends in the longitudinal direction of the beam portion. On the other hand, it is an electrode having a constant width.

According to a fourth aspect of the present invention, there is provided a substrate on which the first electrode is formed, a beam portion that is spaced apart from the substrate and has a constricted portion that is fixed at one end, and is formed on the beam portion. An optical waveguide, an optical functional element formed on the optical waveguide located in the constricted portion, a plurality of second electrodes formed on the beam portion, the pull-in electrode, and the beam A plurality of second electrodes including a stress control electrode whose width is continuously changed with respect to the longitudinal direction of the part, and an optical element control method for controlling an optical element, the pull-in electrode and the first electrode Applying a voltage to each of the pull-in electrode and the first electrode to cause a pull-in in the beam portion so that a predetermined potential difference is generated between the first electrode and the first electrode; The stress control electrode and the first electrode; A step of applying a voltage to control the stress applied to the optical functional element respectively, and having a.

  According to the present invention, it is possible to realize an optical element having an optical functional element that continuously varies the working light band over a wide range.

(A) is a figure (perspective view) which shows the basic structure of the optical element which concerns on the 1st Embodiment of this invention, (b) is the cantilever of the optical element which concerns on the 1st Embodiment of this invention It is a figure which shows the top view of a part. (A) is a figure which shows the calculation result of the maximum principal stress in the fixed end 25 vicinity from the constricted parts 5 and 8 of the cantilever 1 when a voltage is applied to each electrode 21-24, (b) It is a figure which shows the structure of the cantilever 1 and the electrodes 21-23 used for calculation of this largest principal stress, and the applied voltage to each of the electrodes 21-23. It is a figure which shows the deformation | transformation state of a cantilever part, (a) is a figure which shows a state without a deformation | transformation, (b) is a figure which shows a pull-in state, (c) is a figure which shows a large deformation state. . It is a figure which shows the relationship between the tensile stress applied to the optical functional elements 4 and 9, and the band gap variation | change_quantity of the optical functional elements 4 and 9 using germanium. It is a figure which shows the top view of the cantilever part of the optical element concerning the 2nd Embodiment of this invention. It is a figure which shows the top view of the cantilever part of the optical element concerning the 3rd Embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described in detail.

(First embodiment)
FIG. 1A shows a basic structure (perspective view) of an optical element according to the first embodiment of the present invention. FIG. 1B is a plan view of a cantilever portion of the optical element according to the first embodiment of the present invention. The optical element of this embodiment is formed using, for example, an SOI (Silicon on Insulator) substrate. In the optical element, optical functional elements 4 and 9 are formed on a part of the optical waveguides 3 and 7 formed on the cantilever 1 arranged so as to be separated from the substrate 0. The optical waveguides 3 and 7 are connected by an optical waveguide 6, and these optical waveguides have a rib-type optical waveguide structure. The optical functional elements 4 and 9 are formed on the optical waveguides 3 and 7 located at the constricted portions 5 and 8 of the cantilever 1.

  Further, the open end 26 side of the cantilever 1 is provided with an electrode structure including a plurality of electrodes 21 to 23 for controlling the stress application so that the optical characteristics of the optical functional elements 4 and 9 can be continuously changed. ing. The widths of the plurality of electrodes 21 to 23 continuously change in the longitudinal direction of the cantilever 1. Although not shown, it is desirable that electrode pads are prepared outside the cantilever 1 and the electrode pads and the electrodes 21 to 23 are connected by electric wiring.

  A pull-in voltage is applied to some of the plurality of electrodes 21 to 23, and the deformation of the cantilever 1 after pull-in is controlled by the remaining electrodes. Since the stress applied at the time of pull-in is concentrated on the constricted portions 5 and 8 formed on the cantilever 1, the optical functional device fabricated on the optical waveguides 3 and 7 located on the constricted portions 5 and 8 of the cantilever 1. 4 and 9 can be continuously stressed. With such an electrode structure and voltage application method, it is possible to expand a stress control region that can be continuously variably controlled by controlling the voltage applied to each electrode even after pull-in.

  In the optical waveguide 3 (incident optical waveguide) and the optical waveguide 7 (exit waveguide) formed on the cantilever 1, for example, the core material is silicon, the clad material is air, and the rib thickness is the core. A rib-type optical waveguide having a thickness of 200 nm, a rib width (core width) of 400 nm, and a slab thickness of 100 nm. The upper and lower clads of the rib type optical waveguide may be formed of a material having a refractive index smaller than that of a core material such as silicon oxide.

  The optical functional elements 4 and 9 having a quantum well structure formed on the optical waveguides 3 and 7 positioned in the constricted portions 5 and 8 of the cantilever 1 are, for example, germanium having a quantum well thickness of about 10 nm or less. There is a silicon germanium mixed crystal having a quantum barrier thickness of about 10 nm or less.

  The electrodes 21 to 23 formed on the cantilever 1 and the electrode 24 formed on the substrate 0 may be, for example, a metal such as gold, silver, or aluminum, or may be doped with impurities at a high concentration. A semiconductor with a larger thickness may be used.

  Here, the operation of the optical element of the present invention will be described.

  Incident light 2 to the optical element enters an optical waveguide 3 (incident optical waveguide). Light incident on the optical waveguide 3 is subjected to actions such as modulation, light reception, and amplification by the optical functional element 4 having a quantum well structure formed on the optical waveguide 3 located in the constricted portion 5 of the cantilever 1. Light that has been subjected to modulation, light reception, amplification, or the like in the optical functional element 4 enters the optical waveguide 6 (folded optical waveguide) through the optical waveguide 3.

  The folded optical waveguide 6 is a rib-type optical waveguide formed on the cantilever 1, and is, for example, a rib-type optical waveguide in which the core material is silicon and the clad material is air, like the optical waveguides 3 and 7. The light that has passed through the folded optical waveguide 6 enters the optical waveguide 7 (an output optical waveguide).

  Light incident on the optical waveguide 7 is subjected to actions such as modulation, light reception, and amplification by an optical functional element 9 having a quantum well structure formed on the optical waveguide 7 located in the constricted portion 8 of the cantilever 1.

  Through the above process, the incident light 2 is subjected to actions such as modulation, light reception and amplification.

  What determines the working wavelength region of the optical functional elements 4 and 9 is the quantum well structure (size and composition) of the optical functional elements 4 and 9 and the stress applied to the optical functional elements 4 and 9. The stress is controlled by adjusting the voltage applied to the electrodes 21 to 23 formed on the cantilever 1 and the electrode 24 formed on the substrate 0. For example, when a positive voltage is applied to the electrodes 21 to 23 and a negative voltage is applied to the electrode 24, the electrodes 21, 22 and 23 are positively charged and the electrode 24 is negatively charged. Electrostatic attraction occurs. Therefore, the cantilever 1 approaches the substrate 0 and the cantilever 1 is deformed around the constricted portions 5 and 8.

  The electrostatic attractive force at this time is the area of each of the electrodes 21 to 23, the area of the electrode 24, the gap between the cantilever 1 and the electrode 24, the potential difference between the electrode 21 and the electrode 24, and the potential difference between the electrode 22 and the electrode 24. And depends on the potential difference between the electrode 23 and the electrode 24.

  As the potential difference between the electrode 21 and the electrode 24, the potential difference between the electrode 22 and the electrode 24, and the potential difference between the electrode 23 and the electrode 24 are increased, the deformed state of the cantilever 1 “A small deformation state” in which the vicinity of the fixed end 25 is deformed, “a pull-in state” in which the vicinity of the fixed end 25 of the cantilever 1 is deformed and the open end 26 of the cantilever 1 is in contact with the electrode 24, and the cantilever 1 The vicinity of the open end 26 of the cantilever 1 is deformed, and a transition is made to the “large deformation state” after pull-in in which the vicinity of the open end 26 of the cantilever 1 is in contact with the electrode 24.

  Each of the “small deformation state”, “pull-in state”, and “large deformation state” is a unique stable state, and the transition between these states is discontinuous.

  Here, since the constricted portions 5 and 8 are provided in the cantilever 1, the beam deformation generated from the “small deformation state” to the “pull-in state” is absorbed by the deformation from the constricted portions 5 and 8. The voltage applied to each of the electrodes 21 to 24 can be set so that the beam deformation that occurs from the “pull-in state” to the “large deformation state” is absorbed by the deformation near the fixed end 25. Thereby, the variable control range of the stress generated in the vicinity of the fixed end 25 from the constricted portions 5 and 8 of the cantilever 1 can be taken continuously and over a wide range.

  Here, the stress generated in the vicinity of the fixed end 25 from the constricted portions 5 and 8 of the cantilever 1 will be described using an example in which voltages to be applied to the electrodes 21 to 24 are specifically set. FIG. 2A shows a calculation result of the maximum principal stress in the vicinity of the fixed end 25 from the constricted portions 5 and 8 of the cantilever 1 when a voltage is applied to each of the electrodes 21 to 24. FIG. 2B shows the configurations of the cantilever 1 and the electrodes 21 to 23 used for the calculation of the maximum principal stress, and the voltages applied to the electrodes 21 to 23, respectively. For the calculation of the maximum principal stress, the configuration of the cantilever shown in FIG. 2B in which the optical waveguides 3, 7, 6 and the optical functional elements 4, 9 are not installed is used.

  In the calculation of the maximum principal stress, the electrodes 21 on both sides formed on the upper portion of the cantilever 1 with respect to the cantilever 1 having three triangular electrodes whose width decreases in the longitudinal direction of the cantilever 1. , 22 is applied with a potential of 40V as an initial voltage, a voltage of 0V is applied to the electrode 24 on the substrate 0, and a voltage applied to the central electrode 23 formed on the upper portion of the cantilever 1 is in the range of 0V to 150V. The maximum principal stress in the vicinity of the fixed end 25 from the constricted portions 5 and 8 of the cantilever 1 when the potential difference with the electrode 24 on the substrate 0 was increased or decreased was calculated. FIG. 2A shows the calculation result.

  Moreover, the size of each part of each cantilever (FIG. 2B) and each electrode used for the calculation of the maximum principal stress is as follows. The cantilever 1 has a width of 30 μm, a length of 20 μm, a thickness of 0.2 μm, and a material having a Young's modulus of 130 GPa. Two constricted portions 5 and 8 having a width of 5 μm are provided at a portion of 5 μm from the fixed end 25 of the cantilever 1. The distance between the centers of the two constricted portions is 15 μm. The electrodes 21 and 22 on both sides formed on the upper portion of the cantilever 1 have a maximum width of 15 μm, a length of 20 μm, and a thickness of 0.2 μm, which is a complete conductor. The central electrode 23 formed on the upper portion of the cantilever 1 has a maximum width of 30 μm, a length of 20 μm, and a thickness of 0.2 μm, which is a complete conductor. The gap between the cantilever 1 and the substrate 0 is 3 μm.

  From FIG. 2A, it can be seen that a wide range of stress changes can be used by using the large deformation state. In addition, an element using electrostatic attraction as shown in FIG. 1 consumes electric power when the voltage changes, but does not consume large electric power when holding a constant voltage. Therefore, it is desirable to set the pull-in state by some method in advance, shift to the large deformation state with a minimum voltage change, and control the stress in the large deformation state. For example, the voltage applied to the stress control electrode can be reduced by applying a voltage to a part of the plurality of electrodes other than the stress control electrode to obtain a pull-in state in advance.

  In addition, by changing the electrode width in the longitudinal direction of the cantilever 1 and changing the moment generated in the cantilever 1, either a wide range of stress generation or precise stress control is required even with the same applied voltage. Various control methods can be selected.

  Here, the deformation state of the cantilever 1 will be described again. 3A to 3C schematically show no deformation, a pull-in state, and a large deformation state. Here, in order to schematically show the deformation state, the same configuration as the cantilever 1 shown in FIG. 2B, that is, the optical waveguides 3, 7, 6 and the optical functional elements 4, 9 are installed. The simulated deformation state is shown in the configuration that is not. When a voltage of 0 V is applied to the electrode 24 on the substrate 0 and a voltage of 40 V is applied to the electrodes 21 and 22 on both sides formed on the upper portion of the cantilever 1, the cantilever 1 is in a pull-in state (FIG. 3). (B)). After this pull-in state, when a voltage is applied to the electrode 23, a transition is made to a large deformation state (FIG. 3C).

  As shown in FIG. 2A, the initial voltage applied to the electrodes 21 and 22 on both sides formed on the upper portion of the cantilever 1 and the shape and dimensions of various electrodes are appropriately selected to be applied to the electrode 23. The stress generated in the vicinity of the fixed end 25 from the constricted portions 5 and 8 of the cantilever 1 can be controlled continuously over a wide range.

  FIG. 4 shows the relationship between the tensile stress applied to the optical functional elements 4 and 9 and the band gap change amount of the optical functional elements 4 and 9 using germanium. If a tensile stress of 700 MPa can be applied to the optical functional elements 4 and 9, the band gap of germanium can be varied by 100 nm, so that the C band and the L band can be covered with germanium of one composition. Become.

  In the optical element of this embodiment shown in FIGS. 1A and 1B, it is assumed that the electrodes 21 to 24 can set voltages independently. For example, by setting the electrode 24 to 0 V, applying a voltage of, for example, 40 V to the electrodes 21 and 22 in advance to make a pull-in state in advance, and controlling the voltage applied to the electrode 23 independently of the electrodes 21 and 22, The stress generated in the vicinity of the fixed end 25 can be controlled.

  In the present embodiment, as shown in FIG. 1, the electrodes 21 and 22 have a triangular shape whose width increases as they approach the open end 26 of the cantilever 1, and the electrode 23 has the open end of the cantilever 1. 26, the electrode 21 and 22 are not triangular if the width of the electrodes 21 and 22 increases as they approach the open end 26 of the cantilever 1. It may be a trapezoid, a polygon having a plurality of inflection points, or a figure composed of curves. Further, the electrode 23 may be not a triangle, a trapezoid, a polygon having a plurality of inflection points, or a curved line as long as the width of the electrode 23 decreases as it approaches the open end 26 of the cantilever 1. The figure which consists of may be sufficient.

  In the present embodiment, for example, the electrode 21 or 22 is used as a pull-in electrode, and the electrode 23 is used as a stress control electrode. A predetermined constant voltage required in advance is applied to the electrode 21 or the electrode 22, or both the electrode 21 and the electrode 22, so that the cantilever 1 is in a pull-in state. Since the width of the electrode 23 becomes smaller as it approaches the open end 26 of the cantilever 1, the moment load at the time of voltage application becomes smaller than that when the width is constant, resulting in a small stress with a large applied voltage. Change can be obtained. Therefore, it is suitable for applications that require precise stress control, and thus precise band gap control.

(Second Embodiment)
FIG. 5 shows a plan view of a cantilever portion of an optical element according to the second embodiment of the present invention. The configuration other than the cantilever portion (substrate 0 and the like) is the same as in the first embodiment. That is, in the optical element of this embodiment, the cantilever 1 is arranged apart from the substrate 0 having the electrode 24 as in the first embodiment. The difference between this embodiment and 1st Embodiment exists in the shape of the electrodes 21-23 as follows.

  That is, contrary to the first embodiment, the electrodes 21 and 22 have a triangular shape whose width decreases as the open end 26 of the cantilever 1 is approached. As long as the width of the cantilever 1 decreases toward the open end 26, the shape may be a trapezoidal shape, a polygon having a plurality of inflection points, or a figure composed of a curve. good.

  Further, the electrode 23 has a triangular shape whose width increases as it approaches the open end 26 of the cantilever 1. As long as the width of the cantilever 1 increases as it approaches the open end 26, it may be a trapezoid, a polygon having a plurality of inflection points, or a figure composed of curves. good.

  In the present embodiment, for example, the electrode 21 or 22 is used as a pull-in electrode, and the electrode 23 is used as a stress control electrode. A predetermined constant voltage required in advance is applied to the electrode 21 or the electrode 22, or both the electrode 21 and the electrode 22, so that the cantilever 1 is in a pull-in state. Since the width of the electrode 23 increases as it approaches the open end 26 of the cantilever 1, the moment load at the time of voltage application increases as compared with the case where the width is constant, resulting in a large stress with a small applied voltage. Change can be obtained. Therefore, it is suitable for an application that requires a large stress difference and thus a large band gap difference.

(Third embodiment)
FIG. 6 is a plan view of a cantilever portion of an optical element according to the third embodiment of the present invention. The configuration other than the cantilever portion (substrate 0 and the like) is the same as in the first embodiment. That is, in the optical element of this embodiment, the cantilever 1 is arranged apart from the substrate 0 having the electrode 24 as in the first embodiment. In the present embodiment, a rectangular electrode 32 is disposed in the vicinity of the open end 26 on the cantilever 1, and the width of the triangle becomes smaller as the open end 26 of the cantilever 1 is closer to the fixed end 25 than the electrode 32. An electrode 31 having a shape is arranged. The electrode 31 may be a trapezoid, a polygon having a plurality of inflection points, or a curved line as long as the width of the electrode 31 changes as it approaches the open end 26 of the cantilever 1. The figure to be made may be used.

  In the present embodiment, for example, the electrode 32 is used as a pull-in electrode, and the electrode 31 is used as a stress control electrode. A predetermined constant voltage required in advance is applied to the electrode 32 to keep the cantilever 1 in a pull-in state. Since the electrode 32 is in the vicinity of the open end 26 of the cantilever 1, it can be brought into a pull-in state with a smaller voltage compared to the first or second embodiment. Therefore, it is suitable for applications where it is difficult to supply a large voltage.

  In each of the above-described embodiments, the configuration examples including the optical functional elements 4 and 9 on the optical waveguides 3 and 7 positioned in the constricted portions 5 and 8 of the cantilever 1 are shown. It is good also as a structure provided with an optical function element only on any one of the optical waveguides 3 and 7 located.

DESCRIPTION OF SYMBOLS 0 Board | substrate 1 Cantilever 2 Incident light 3, 6, 7 Optical waveguide 4, 9 Optical functional element 5, 8 Constricted part 10 Output light 21-24, 31, 32 Electrode 25 Fixed end 26 Open end

Claims (4)

A substrate on which a first electrode is formed;
A beam portion disposed at a distance from the substrate and having a constricted portion with one end fixed;
An optical waveguide formed on the beam portion;
An optical functional element formed on the optical waveguide located in the constricted portion;
A plurality of second electrodes formed on the beam portion, the plurality of second electrodes including a pull-in electrode and a stress control electrode whose width is continuously changed in the longitudinal direction of the beam portion. Electrodes,
A voltage is applied to each of the pull-in electrode and the first electrode so that a predetermined potential difference is generated between the pull-in electrode and the first electrode, and pull-in is generated in the beam portion, An optical element, wherein after applying the pull-in, a voltage is applied to each of the stress control electrode and the first electrode to control a stress applied to the optical functional element.   2. The optical element according to claim 1, wherein the pull-in electrode is an electrode whose width is continuously changed in the longitudinal direction of the beam portion, contrary to the stress control electrode.   The pull-in electrode is an electrode that is positioned closer to the open end of the beam portion than the stress control electrode and has a constant width in the longitudinal direction of the beam portion. Optical element. A substrate on which the first electrode is formed; a beam portion disposed at a distance from the substrate and having a constricted portion with one end fixed; an optical waveguide formed on the beam portion; and the constricted portion An optical functional element formed on the optical waveguide, and a plurality of second electrodes formed on the beam, the pull-in electrode, and the longitudinal direction of the beam continuously A plurality of second electrodes including a stress control electrode whose width has changed, and an optical element control method for controlling an optical element comprising:
Applying a voltage to each of the pull-in electrode and the first electrode so as to generate a predetermined potential difference between the pull-in electrode and the first electrode, thereby generating a pull-in in the beam portion;
Controlling the stress applied to the optical functional element by applying a voltage to each of the stress control electrode and the first electrode after causing the pull-in;
An optical element control method comprising:

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